Social movements must mobilize participation from bystanders to survive, yet there is little research on how bystanders' evaluations of social movements predict their likelihood to join. Charles Tilly offered a four-part theoretical "scorecard" by which people evaluate movements: worthiness, unity, numbers, and commitment. The authors created a novel and psychometrically valid measure (WUNC-12) and then used three online experiments to test its predictive validity for participatory action. They found broad support for WUNC as a mediating mechanism and show that WUNC perceptions are correlated with impressions of the legitimacy and efficacy of a movement. Finally, they found that movements that simultaneously signal a single-issue focus and the presence of a demographically heterogeneous set of members elicit greater WUNC perceptions and higher intentions to mobilize. With these results taken together, the authors demonstrate how social movement signaling translates into WUNC perceptions, which in turn mediate how signaling leads to social movement support and mobilization.
